When Is Leap Year

What this tool does

This is the quickest way to answer "when is the leap year." One tap and it tells you three things: the most recent leap year, whether this year is one, and the next leap year coming up. There is nothing to type in. It reads the current year and works the rest out, so you get your bearings in the leap-year cycle straight away.

How to use it

1. Press Check Leap Years. That is the whole of it.

The last leap year, the status of the current year, and the next leap year all appear together.

How it works it out

It starts from this year and checks it against the leap-year rule, a year being a leap year if it divides by 4, with century years needing to divide by 400 as well. From there it steps backward a year at a time until it lands on the previous leap year, and forward until it reaches the next one. Because the rule is fixed, those answers are exact rather than estimates.

Where you are in the four-year cycle

Leap years arrive every four years almost without fail, so the next one is rarely more than three years off, and knowing the last and next pair tells you exactly where the current year sits between them. The only wrinkle is the century years, where the divide-by-400 part of the rule can stretch the usual four-year gap to eight, as happened around 1900. For any year you are likely to care about day to day, though, the steady four-year rhythm holds, and this tool shows it at a glance.

Why people check

Often it is about the 29th of February itself. Knowing whether this year has one, when the next one falls, or planning something around the date, including birthdays for the people born on it who only get a true birthday every four years. It is also just a satisfying thing to confirm when the question pops into your head.

Questions people ask

When is the next leap year?

Press the button and the tool shows the next leap year from now, along with the last one and whether the current year qualifies.

Is this year a leap year?

The tool checks the current year against the rule and tells you yes or no, as part of the same result.

Is it always four years between leap years?

Almost always. The exception is around century years that are not divisible by 400, where the gap can be eight years, as it was between 1896 and 1904.

What about people born on 29 February?

Their birth date only lands on the calendar in leap years, so this tool is a handy way to see when their next true birthday falls.

References

1. U.S. Naval Observatory, Astronomical Applications Department: Leap Years. https://aa.usno.navy.mil/faq/leap_years